Signaling system



May 17, 1932. F. E. T ERMAN SIGNALING SYSTEM Filed May 10, 1929 r 0 4-4 F F 66' INVENTOR pe fze/Ck EM/VO/VS TEe/VAIV m j Gila/1.4

ATTORNEY Patented May 17, 1932 FREDERICK EMMONS TEE-MAN, OF STANFORD UNIVERSITY, CALIFORNIA SIGNALING SYSTEM Application filed May 10,

My invention relates to signaling systems in which the signal to be transmitted is modulatedupon a carrier current or oscillation of high frequency, and particularly to radio 5 communication systems and its broad OlJJQCt is to increase the numbers of messages which can be carried by alimited band of frequencies. i

An object of my invention is to provide a 1,0 means of generating a plurality of-carriers l in closely adjacent communication channels without interference between these channels.

Another object of my invention is to provide means of generating a plurality of elec* ,1 trical oscillations having a constant frequency difference.

Still another object of my invention is to provide a means of operatingan extensive radio net with a single unified frequency con- ,ao trol. I

.A further object of my invention is to provide a means whereby communication channels may be spaced more closely than is possible by even thebest of the'present labora- 1 tory methods of frequency control.

My invention posseses other objects and valuable features, some of which will be set forth in the following description of my invention which is illustrated in the drawings ,30 forming part of the specification. Itis to be 4 understood thatI do not limit myself tothe showing made by the said description and drawings, as I may adopt varying forms of my invention within the scope of the claims.

Radio communication channels are now assigned on' a basis which has for one of its factors the precision with which the carrier frequency can be controlled. This precision of control expressed in cycles or kilocycles is proportional to the nominal frequency of the carrier channel itself and therefore as the frequency of the channel becomes higher, the channels are more widely spaced.

The actual frequencies or side bands= which are used in transmitting a message are independent of the modulated frequencies.

For telegraph service this side band varies from 200 cycles wide to about 35 cycles wide,

depending upon the code used and the method 5,0 of reception. Thus, for high frequency radio 1929. Serial N0. 361,911.

telegraphy, that is, for communication at fre'quenciesin the neighborhood of ten thousand kilocycles, the assigned channels are several thousand cycleswide, of which only a few'hundred cycles are actually used, since closer spacing would result in overlapping of adjacent channels'and confusion of signals due to frequency instability of the transmitters; j I --Broa-dly considered, my invention comprises the'generation of a master oscillation, whose frequency is, of course, preferably held as stable as possible. Fromthis oscillation are derived a plurality of other oscillations whose frequencies differfrom the master-fie quency by fixed amounts, and these derived frequencies are independently keyed or otherwise modulated. The result is that if the master'frequency varies, theothers vary in the same direction and tothe same degree, so 70 that there is no overlapping of channels or garbling of messages. One oscillation of the series thus generated may be transmitted unmodulated,"and used to control the frequency of a generator at the receiving station. Here, the same method'may be used to generate'a frequency of a constant difference from the master frequency, which the receivingstation may, in turn, use for transmission. The preferred method of'derivingthe secondary frequencies from the'master frequency is to use the master frequency oscillation to generate a rotating magnetic field within which an inductor or coil is mechanically rotated.

There will then be generated Within the'coil 85 a -.frequency proportional to the algebraic d-iflerence between the frequency of rotation of the'magnetic field and the product of the frequencyof otation-of the" coil and the number of pairs of field poles. Referring to the drawings:

Figure 1 is a diagram illustrating 'th'e method of generating the series of carrier waves; 1 I y Fi re 2 is a schematic diagramshowing a rac io net whose frequencies are controlled by a single master station and embodying this invention. i i

In more detailed terms the embodiment of my invention which I have -chosen-for de- 7 llli) tit - communication band which it is desired to use. Across the output leads 7 and 8 of the oscillator is connected a phase splitter, comprising a resistor 9 and a condenser 11, across which are connected the vacuum tube amplis fiers 12 a n l 13. Thcimpedances of the re sistor andconde'nser are so-chosen'as to make the voltage drop across the two substantially equal, but differing in phase by ninety degrees- V r The output circuits of the two amplifiers are connected across the coils 14,v 14 and 15, 15respectiyely, andthese coils arefplaced at substantially r'ightangles so as'to provide a magnetic field of uniform strength andro tating in space at the frequencygenerated bythe oscillator 6. q a

Rotat'ably mounted upon the shaft 17 with in the rotating field, and driven-by a constant speed motor 18, is an inductor 19 whose terminals are brought .totheslip 'rings or other collector device 21. 2 Brushes 22, hear; ing upon theslip-rings, connect thruthe leads 23 to the input of amplifier 24 which is connected to an antenna- 26 andlcounterpoise 27. or otherv suitable .radiatingsystem. A key 28 or other suitable device is used in the customary manner for modulatingthe output of the amplifier 24,- r

if both the rotating field and the inductor 19 rotate in the same direction there will be generated in the inductor a current whose requency is equal to the difference ofthe two frequencies of, rotation. If the I directions of rotation of field and inductor are opposite, the frequency of the generated current. will be the sum of the two frequencies of rotation. I f the speed of rotation of-the motor be one hundred revolutions per second, the-frequency generated in the inductor 19 will difs-s fer from that of theoscillator 6 by exactly this amount. The speed of the motor may easily be controlled to within one per cent of its required value, that is,-:to within one revolution per second, plusorminus; but-to control a separate oscillator operating in the short wave telegraph band tothis accuracy, i. e-., to one cycle per second, the precision of control would have tobenot to one per cent, but to within oneshundred=thousandth of one per cent, and such stability of control is as yet impossible of coinmercialattainment.

:Itis of course possible: to hold j the' inductor stationary and rotate the field coils me- 1 chanically This method, although identical in principle with that described, ofiers me chanical difiicul ti es which makethe described method preferable. Electrostatic fields may also be used in place of the ma'gneti'c fields here described. 7 1.

windings differs from that of the oscillator by twicethc speed of rotation of the shaft 17 upon which the inductor is mounted, for reasons well understood in electrical art. In the present case, under the assumptions made above, this frequency would differ from that of the oscillator 6 by two hundred cycles per second, and from that generated in the in ductor 19 by one hundred cycles per secondi Thecurrent generated in the inductor 41 is shown as brought out thru the collector rings 42 and brushes 43' and the leads 44 to the amplifier {16, thence to be radiated bythe antenna system 47 without modulation. The reason for this will be discussed later.

" By mounting a plurality of coils upon the shaft 17, each provided with its own field coils, some of whichare arranged to produce clockwise rotational fields while others produce counter-clockwise fields, the series of oscillations, each differing from the adja cent oscillation by a fixed amount, may be extended as far as desired. It is moreover unnecessary to increase the number of poles in order to extend the series, as a portion-of the output of each inductor may be used to excite the succeeding field.

Succeeding field coils should be separated by electrostatic shielding 48.

It will be noted that the oscillator 6 shown as being provided with an antenna system 51 towhich it may be connected by a switch 52. The oscillator 6 may therefore be used eitheras a self-excited oscillator controlling the-entire communication system,

2, where. a master station 55 radiates a plu- :7

generated as shown in Figure 1.

One of these frequencies, preferably an rality of waves of closely adi acent frequencies c'nd frequency in the series radiated, is 'transmitted unmodulate'd, and is picked up by the secondary stations 5 6, 52 and58 and used to control their own master oscillators. This frequency is here assumed to be the master iio frequency minus four hundred cycles, and is m indicated the lines 61 which are marked F t00. The frequency F-200 is modulated and used. to transmit to station 56, as indicated bythe line 62, while the frequency F is used to transmit to station 57 and F-l- 200 to st'a'tion58, indicated by lines 63 and 64 its respectively. The secondary stations use the received unmodulated frequency F4O0 to heterodyne the received waves from station 55, the particular signal corresponding to their own communication channel being separated by electrical acoustic or mechanical filters.

The secondary stations control the frequency of their master oscillators by means of the received umnodulated waves F -400, and derive their all transmitting frequencies therefrom in the same manner that the master station derives its transmitting frequencies from the frequency F. Station 56 transmits on the frequency F-400. as is indicated by the line 66. Station 57 transmits on the frequency F+600. as indicated by the line 67, and station 58 on the frequency F +800, as indicated by the line 68. Additional stat-ions or additional communication channels for the stations shown, may be added as desired.

The use of an end frequency of the series as the heterodyning or controlling frequency is advisable because the use of a frequency in the middle of the bands would give the same beat frequency with stations both above and below it in the bands, and their separation from each other would therefore be extremely diflicult.

This system is capable of almost indefinite extension. I f the separation desired between the communication channels is greater than can conveniently be supplied mechanically, it is possible to derive the transmitting frequencies from a master frequency which is integrally divisible into a frequency in the transmitting band. A difference frequency having the same ratio to the desired frequency diflerenee as the master frequency has, to the transmission frequency selected is mechanically generated, and both master and difference frequencies are multiplied by means of harmonic amplifiers. I

It is also possible to generate one series of difference frequencies as described. and bv heterodyning this series by a frequency with. in the series. to produce a second series founded upon a sum frequency. In the system described above. the frequency F could be used as a heterodyne frequency to produce a series comprising the frequencies 2 F-400, 2 F-200. etc.

It is also possible to heterodyne the frequency series with some frequency lying outside of the band. but in this case the frequency instability of the new series, thus obtained. will depend uponthe frequency shift of both oscillators, and therefore will not follow exactly in step with the series directly generated. as in the other cases here mentioned. The difference between successive frequencies of the series will remain constant, however.

The use of the method here out-lined enables a single communication channel to be used much more'effectively tha'n'has heretofore been possible. The method may be ex.

tended into adjacent frequency channels with fields, and it has therefore been considered, r

unnecessaryto describe the component parts in detail. Thus, the coils for establishing the rotating field and the rotating inductor form what is essentially a radiogoniometer, such as is familiar in radio beacon and direction finding work, the only difference being that the phases in the coils differ, and the inductor is continuously rotated instead of set to a desired azimutln Speed controlled motors have been developed for picture transmission, electric clocks. and other uses, .and suitable oscillators and amplifiers of many suit able types are well known.

Methodsof modulation or keying may. vary from the hand operated key to printer telegraph or voice modulation without affecting the principles of the system. If key modulation is used, howevenit is advisable to make the modulating wave rounded instead of rectangular, in orderto limit the width of the sidebands and reduce keythump on adjacent bands. This is also a well known expedientwhich need notbe described in detail here. i

I claim: 1'. The method of U signaling which comprises generating a master oscillation, generating a rotating field with said oscillation, rotating an element in said field to produce a second'oscillation of different frequency, and transmitting both of said oscillations.

2. The method of signaling which comprises generating a master oscillation, generating a rotating fieldwith said oscillation, rotating an element in saidfield to produce a second oscillation of different frequency, modulating one of said oscillations and transmittingboth of said oscillations.

3.'The method of signaling which come prises generating a master oscillation, gencrating a rotating field with said'oscillation,

rotating an elementinsaid field to produce a second oscillation of different frequency,

keying .one of said oscillations, and trans- V mitting both of said oscillations; i

{4. Themethod of signaling which com,- prises generating a master oscillation, generating a rotating field with said oscillation, rotating an element in saidfield to produce a second-oscillation whose frequency is the algebraic difference of the frequencies of r0,- tation of said field and said element and transmitting both of said oscillations.

5. The method of signaling which comprises generating a master oscillation, generating a rotating field with said oscillation, rotating an element in said field to produce a second oscillation of different frequency,

and using each of said oscillations to control the frequency of an electric Wave transmitter. V

6. The method of signaling which comprises generating a master oscillation, gencrating a rotating field with said oscillation, rotating an element in said field to produce a second oscillation hose frequency is the algebraic difference of the frequencies of rotation of said field and said element, and using each of said oscillations to control the frequency of an electric Wave transmitter.

7. The method of signaling Whichco'mprises generating a master oscillation, inducing a series of oscillations of different frequency therefrom by rotational difference, and using each oscillation of said series to control the frequency of an electric Wave transmitter. i

8. The method of signaling which comprises generating a master oscillation, inducing a' series of oscillations ofdifl'erent frequency therefrom by rotational dilference, modulating certain of said oscillations, and transmitting said oscillations.

9. The method of ,signal'ng which c0mprises generating a master oscillation, inducing a series of oscillations of different frequency therefrom by rotational difference, modulating all but one of said series, and transmitting said series.

10. The methodof signaling which com-' prises generating a master oscillation, inducing aseriesof oscillations of different frequency therefrom by rotational difference, modulating all but an end frequency oscillation of said series, and transmitting said series.

11. The method ofsignaling which comprises generating a master oscillation, generating an electrically rotating field with said oscillation, causing a relative mechanical rotation between said field and an inductor element to" generate an oscillation of different frequency, and usingeach of said oscillations to control the frequencyof an electric wave transmitter. l i a 12. A radio transmittercomprising means for generating an electrical oscillation of a master frequency, means for producing an electrically rotating field excited by said oscillation, an inductor mounted Within said field, m'eansfor causing a relative rotation between said field producing means and said inductor to produce an oscillation of different frequency,- and means controlled' by said second oscillation for-radiating an electromagnetic Ware.

13. A radio transmitter comprising means forgenerating an electrical oscillation of a master frequency, means for producing an 

